1. Field of the Invention
The present invention relates to a mutant strain of Streptococcus thermophilus having a defective lactose transport system. The organism has utility in food and commercial applications where a reduction of lactose is sought.
2. Description of the Prior Art
.beta.-galactosidase (.beta.-D-galactoside galactohydrolase, EC 3.2.1.23) hydrolyzes lactose to its hexose components, glucose, and galactose. .beta.-galactosidase is used commercially primarily in the food industry to eliminate lactose from dairy products. In a large segment of the world's population, lactose is poorly digested. Additionally, lactose has limited solubility in water resulting in undersirable crystallization in concentrated dairy foods. Since lactose has only one-fifth the degree of sweetness of sucrose, the use of whey concentrates or whey powder in processed foods has been limited.
Presently, .beta.-galactosidase for food applications is available from various yeast and fungal sources. The enzymes that are used most extensively are those from Kluyveromyces fragilis and Kluyveromyces lactis. Unfortunately these enzymes do not tolerate the high temperatures used under industrial conditions.